sched: Remove unused PF_ALIGNWARN flag

PF_ALIGNWARN is not implemented and it is for 486 as the
comment.

It is not likely someone will implement this flag feature.
So here remove this flag and leave the valuable 0x00000001 for
future use.

Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20100913121903.GB22238@darkstar>
Signed-off-by: Ingo Molnar <mingo@elte.hu>